1. Field of the Invention
This invention relates to a combination air conditioning and heating unit and more particularly to a method and apparatus for minimizing corrosion of heat exchangers by substantially reducing the formation of condensate on the heat exchanger during the cooling season.
2. Description of the Prior Art
Conventional combination air conditioning and heating units include burners which mix a supply of gas and air in the Venturi section of the burner and direct this mixture into the combustion chamber where it is typically open to the atmosphere to provide ambient air for a combustible mixture. The mixture is ignited and combustion takes place in the combustion chamber. In such conventional arrangements the burner is located beneath the heat exchanger and the combustion products rise upwardly through the heat exchanger and are discharged to the atmosphere. The heat exchanger is formed to accommodate the flow of the gas from the combustion chamber into contact with one side of the surfaces of the heat exchanger. The apparatus of the foregoing type also includes a fan assembly for directing air over the opposite side of the surface of the heat exchanger. Heat generated by the combustion products is transferred through the heat exchanger surfaces, which are usually metal, to the air circulated over the heat exchanger surface by the fan.
The apparatus also comprises a compressor, a condenser and an evaporator connected into a closed circuit to provide air conditioning during periods when the burner is not operating.
During the cooling season when the heat exchanger is not operable, a relatively warm ambient air passes from the combustion chamber which is open to atmosphere, through the interior of the heat exchanger. When the evaporator is operable, for air conditioning purposes, the chilled air which has passed over the evaporator or the returned air from the building is brought into contact with the outside surface of the heat exchanger. As a consequence of cooling the tubes of the heat exchanger by the passage of cooled air from the evaporator, or from the building, the temperatures of the inside surfaces of the heat exchanger may be so low as to be below the dew point of the ambient air passing within the tubes of the heat exchanger. Under such conditions, moisture from the ambient air passing through the heat exchanger will be condensed on the inside walls resulting in the corrosion of the heat exchanger casing.